A sensorless control method performed based on induced voltage with use of an adaptive observer or the like is known as a method for controlling an AC rotary machine such as a synchronous machine or an induction machine. The sensorless control method based on induced voltage has a feature that a position sensor or a velocity sensor can be omitted. However, in a low-speed rotation region, induced voltage is small and therefore it is difficult to detect or estimate induced voltage. Thus, there is a problem that the drive characteristics deteriorate in a low-speed rotation region.
On the other hand, in a low-speed region, by performing control based on a result of position detection using saliency of inductance while superimposing voltage or current having a frequency different from a fundamental frequency of an AC rotary machine, it becomes possible to perform driving in a low-speed region even by a position sensorless control. However, in the case of performing driving in a high rotation region by using saliency of inductance, there is disadvantage in operation efficiency, voltage usage rate, and maximum current because of occurrence of voltage or current other than a fundamental wave.
Considering the above, if an AC rotary machine is driven based on a result of position detection using saliency of inductance and the AC rotary machine is driven by sensorless control using induced voltage in a high rotation region, it becomes possible to provide a device that can be driven in the entire speed region with low cost. In this case, it is important to perform smooth driving over a range from a low-speed region to a high-speed region.
For making it possible to smoothly drive an AC rotary machine over a range from a low-speed region to a high-speed region, the following invention is disclosed, for example.
In order to appropriately generate a phase in a rotational dq coordinate system required in a vector controller basic section without using a position sensor, a low-frequency region phase generator for generating a phase for low-frequency region and a high-frequency region phase generator for generating a phase for high-frequency region are provided, and further, a phase synthesizer for synthesizing these two kinds of phases by averaging them in a weighted manner in terms of frequency is provided, whereby the synthesized final phase is used as a phase in a rotational dq coordinate system (for example, see Patent Document 1).
In addition, the following invention is disclosed. In a sensorless control method for performing continuous control over a range from zero speed to a high-speed region of an AC electric motor, control is performed by using a velocity estimated value west and a position estimated value θ0 estimated by a mechanical mathematical expression model by a position and velocity estimation device, so that position error Δθ obtained by calculation of a cross product of a first magnetic flux vector calculated by using a rotor angle and a second magnetic flux vector calculated without using a rotor angle becomes zero (for example, see Patent Document 2).